Process of producing articles from cellulose acetate



- said proposals, for instance, their strength and Patented Oct. 15,1940 UNITED STATES.

os'a'rwms mom raocsss or raonucm caummsa scsrs'ra Emil Hubert,Dessau-Ziebigk, and Bureau 1101- mann and Heinrich Pabst, Donnagen,Germany, assignors to I. G. Farbenindustrle Aktiengesellschsit, manyFrankfort-on-the-Main, Gel- No Drawing. Application January 14, 1936,Se-

rial No. 184,968. 193':

This invention relates to a process of -producing shaped articles fromcellulose acetate and more especially from cellulose acetate which issoluble in chloroform. It is known to produce shaped articles forinstance, fibres or threads,

from acetone soluble cellulose acetate by spinning a solution 'ofhydrolized and thereafter precipitated cellulose acetate according toeither the dry or the wet spinning method. It has also been tried toproduce in a similar way shaped articles from cellulose acetate whichhas not been hydrolized to the acetone soluble stage, butwhich is stillsoluble in chloroform like the primary acetate obtained in the customaryacetylation processes. However, the hitherto made proposals of this kindmet with great dimculties. Clogging of the filters and nozzles of thespinning machines and breakage of the filaments very frequentlyoccurred, thereby making the continuous operation of the spinningprocess impossible. Moreover, the mechanical prop erties of thefilaments obtained according tothe extensibility, and also their lusterand softness did not come up to the present high practical standards.

It is an object of our inventiton to furnish a method of producingshaped articles from chloroform-soluble cellulose acetate which will notgive rise to the above-mentioned'difficulties anddisadvantages and whichwill yield high quality products which will stand any competition in themarket. In the following our invention will be described moreparticularly as applied to the manufacture of fibres and filaments fromchloroform-soluble cellulose acetate. However, it will be easilyunderstood that the invention may also be applied to the production ofother shaped articles like, for instance, bands, films, foils,artificial horse hair and so on. The process according to our inventionmay. be shortly summarized as follows:

A crude solution, of cellulose acetate as primarily obtained byacetylating cellulose, after rendering the acetylation catalystinefl'ective and establishing the desired cellulose acetate content, isheated to higher temperatures and is thereupon spun into an aqueousinorganic salt solution of lower temperature. Further particulars of ourinvention will be apparent from the following more detailed descriptionthereof.

It is of particular significance for the usefulness of our new processthat it allows spinning crude cellulose acetate solutions, 1. e., thesolutions as they are primarily obtained in the cus- January 19,'lClaims. '(ci. rs-so tomary acetylation processes 'of' cellulose; It isonly necessary to-render the acetylation catalyst (which in mostcases issulfuric acid) ineffective; so that during the further stages ofmanufacture the catalyst has no injurious action on thecellulose'acetate' solution or on the finished products. It will beunderstood that in this respect those -crude cellulose acetate solutionsare especially suitable for use in the present process which have beenprepared in the presence of 10 small amounts, of catalyst acid, as, forinstance, in the acetylation process using methylene chloride in theacetylation mixture as described in the U. 8.- Patent No. 2,126,190. 1

It is not absolutely necessary that the acetic acid content of thecellulose acetate corresponds to the theoretical value of primarycellulose acetate (cellulose trlacetate), i. e., 62.5%. On the contrary,the solutions are more easily to be spun if a slight hydrolysis has beenperformed 20. which, however, should not go so far as to change thesolubility of the cellulose acetate; the latter should still be solublein chloroform and substantially insoluble in acetone. This means thatthe acetic acidcontent ,of the cellulose acetate 2 may vary betweenabout 59% and the theoretical value; preferably the acetic acid contentis between about 60 and 61.5%.

When the crude solutions have been hydrolized the acetylation catalystis made ineffective by neutralization which may be performed with anysuitable agent. In order to avoid as much as possible precipitationstaking place in the spinning solution which might clog the filters andnozzles and give rise to rupture of the filaments, 86 it has proved tobe advantageous to use such neutralizing agents which form with thecatalyst acid compounds which can not be removed from the celluloseacetate solution by filtration since they are either so well solubletherein as not to 40 form precipitates at all, or are forming colloidalprecipitates which pass all filtration equipments without disturbance.Such neutralizing agents are, for instance, on the one hand, aliphaticbases or the salts thereof with weak acids, like 45 propylamine,isobutylamine, diisobutylamine, triethanolamine, and on the other hand,bariumhydroxide or the salts thereof with weak acids, like, forinstance, barium acetate.

Thereupon the crude cellulose acetate solution 50 is brought to asuitable cellulose acetate content. It has been found that our processis working especially well if the cellulose acetate concentration of thespinning solution is between about 12 and 16%. Furthermore, a smallcontent of as methylene chloride and water (from about 2 to 6%) in thespinning solution has a beneficial actionon the spinning process.

As usual, for obtaining special effects other substances like fillingagents, softening agents, dulling agents, dyestuffs and so on may beadded to the spinning solution.

Thereupon the cellulose acetate spinning solution is heated to atemperature which is higher than the temperature of the precipitatingbath. How much the spinning solution should be heated in order toestablish the most favorable conditions for spinning depends somewhat onthe concentration or the viscosity res ectively of the spinningsolution. Ifspinning solutions of higher concentration or higherviscosity are used, they are preferably warmed to 70 to 80 or even 90C., whereas, if working with spinning solutions of lower concentrationor viscosity it may be sufficient to heat them to about 50 to 60 C.

The heated spinning solution is then extruded, for instance through oneof the customary spinning nozzles into an aqueous inorganic saltsolution which in comparison with the spinning solution is of lowertemperature. Many kinds of inorganic salt solutions may be employed forthis purpose which partly have been proposed already in literature, forinstance, solutions of sodium acetate or calcium chloride. As especiallyvaluable we have found, however, aqueous solutions of ammonium salts.The concentration of these precipitating solutions may vary within widelimits, for instance, between about 10 to 30%; their temperature may goup to about 30 to 40 C.

The precipitating liquid is preferably caused to act on the precipitatedfilaments in countercurrent, the quantity and the velocity thereof beingso chosen that the acetic acid content of the precipitating liquidincreases up to to 30%. On observing these conditions, there areobtained filaments of very good mechanical and textile properties, forinstance, strength, extensibility, luster and softness. Moreover, theacetic acid can bemore easily recovered from the solutions whichthemselves are of relatively high acetic acid concentration.

By the concurrent action of the previously described features of ourinvention it is now possible to manufacture shaped articles from crudecellulose acetate solutions of high quality in a simple and economicalmanner. For instance, fi amentscan be produced having a titre of from3.5 to 4.5 den., a breaking strength of 1.3 to 1.7 gr. per demand anextensibility of to 40%. An outstanding problem of cellulose acetatemanufacture has thereby found its solution.

Example 1 100 parts of cellulose which have been bleached and pretreatedin the usual manner are acetylated with a mixture of 2'75 parts aceticacid anhydride, 400 parts methylene chloride and 1.3 parts sulfuric acid(specific gravity 1.84). When the reaction is complete the excessanhydride is destroyed by adding 50 parts of 50% aqueous acetic acid.The solution is then hydrolized, by heating to 50 to 60 C. for 2 to 6hours to an acetic acid content of the cellulose acetate of 60 to 61%.After neutralizing the catalyst, the excess methylene chloride isdistilled off, the solution brought to a content of 14% acetylcellulose, 2% methylene chloride, 3% water and 81% acetic acid,filtrated and deaerated. On its way to the spinning nozzle the solutionis heated in a double-walled pipe by means of hot water (of 70 to 80 C.)and spun into a 20% aqueous chloride solution of C. which is acting incountercurrent on the precipitated cellulose acetate. The rate of flowof the precipitating solution is so chosen that its acetic acid contentnear the spinning nozzle increases up to 17 to 20%.

Example 2 solution is caused to act on the filaments of celluloseacetate in such a manner that its acetic acid content near the spinningnozzle increases up to 20 to 25%.

Example 3 A filtrated and deaerated spinning solution prepared asdescribed in Example 1 and having a content of 13% acetyl cellulose, 2%methylene chloride, 3% water and 82% acetic acid is heated on its way tothe spinning nozzle to 55 to 65 C. and spun into a bath of 15% aqueousammonium chloride and having a temperature of 15 C., the said bathacting in countercurrent on the precipitated filaments of celluloseacetate.

Example 4 A spinning solution as described in Example 3 is heated beforeentering the spinning nozzle to '70 to 80 C. and spun in countercurrentinto a 20% aqueous common salt solution of C.

Example 5 A cellulose acetate spinning solution as described in Example1 is heated to 70 to 80 C. and is thereupon spun through a spinningnozzle into a 30% aqueous ammonium acetate solution oi C.

Instead of into an ammonium acetate solution, the cellulose acetatesolution may also be spun with a similar effect into a 20% aqueoussodium sulfate solution.

We claim:

1. Process of producing shaped articles from cellulose acetate solublein chloroform which comprises heating a crude acetic acid solution asprimarily obtained by acetylating cellulose to a temperature above 50 C.and spinning it into an aqueous inorganic salt solution of a temperaturebelow C.-

2. Process of producing shaped articles from cellulose acetate solublein chloroform which comprises hydrolizing a crude acetic acid solutionas primarily obtained by acetylating cellulose until an acetic acidcontent of not less than 59% is reached, heating said solution to atemperature above 50 C., and spinning it into an aqueous inorganic saltsolution of a temperature below 40 C.

3. Process of producing shaped articles from cellulose acetate having anacetic acid content of from 59 to 62.5% which comprises rendering theacetylation catalyst of the crude solution as primarily obtained byacetylating cellulose ineffective, bringing the solution to an acetatecontent of about 12-16%, heating it to a temperature above 50 C., andspinning it into an aqueous inorganic salt solution of a temperaturebelow 40 C.

4. Process of producing shaped articles from cellulose acetate solublein chloroform which comprises rendering ineffective the acetylationcatalyst in the crude solution of cellulose acetate as primarilyobtained by :acetylating cellulose, bringing the solution to an acetatecontent of about 12-16%, heating it to a temperature above 50 C-., saidsolution containing of from 2-6% of Water and methylene chloride, andspinning it into an aqueous inorganic salt solution of a temperaturebelow about 40 C.

5. Process of producing shaped articles from cellulose acetate having anacetic acid content of from 59-62.5% which comprises renderingineffective the acetylation catalyst contained in the crude acetic acidsolution as primarily obtained by acetylating cellulose, bringing thesolution to an acetate content of about 12-16%, heating it to atemperature above 50 0., said solution containing of from 2-6% of waterand methylene chloride, spinning it into an aqueous inorganic saltsolution of a temperature below about 40 C., and leading the saidinorganic salt solution in a coun'tercurrent to the flow of theprecipitated cellulose acetate.

6. Process of producingshaped articles from cellulose acetate having anacetic acid content of from 5962.5% which comprises renderinginefiective the acetylation catalyst contained in the crude acetic acidsolution as primarily obtained by acetylating cellulose, bringing thesolution to an acetate content of about 12-16%, heating it to atemperature above 50 C., said solution containing of from 2-6% of waterand methylene chloride, and spinning it into an aqueous. solution of anammonium salt of a temperature below about 40 C., and leading the saidammonium salt solution in countercurrent to the flow of the precipitatedcellulose acetate.

7. Process of producing shaped articles from cellulose acetate having anacetic acid content of from 59-62.5% which comprises renderinginefiective the acetylation catalyst contained inthe crude acetic acidsolution as primarily obtained by acetylating cellulose, bringing the.solution to an acetate content of about l2l6%, heating it to atemperature above 50 C., said solution containing of from 2-6% of waterand methylene chloride, and spinning it into an aqueous solution of anammonium salt of a temperature below about 40 C., and leading the saidammonium salt solution in countercurrent to the flow of the precipitatedcellulose acetate in such a manner that the acetic acid content thereofincreases up to from 15-30%.

EMIL HUBERT.

RUDOLF HOFMANN. HEINRICH PABST.

